Volkswagen, trying to get to the bottom of its emissions-cheating scandal, on Thursday pressured employees to tell what they know, announcing an amnesty program for informants that will expire at the end of the month.

The company has yet to explain publicly who was responsible for installing software in 11 million diesel vehicles that was designed to disguise the output of nitrogen oxide, a pollutant harmful to the lungs. Volkswagen also admitted, just last week, that it underreported the levels of carbon dioxide produced by about 800,000 of its diesel and gasoline vehicles in Europe and that had it exaggerated their fuel economy.

In a letter to employees on Thursday, Herbert Diess, chief executive of the division that produces Volkswagen brand cars, said people who provided information would not be fired or face damage claims. Mr. Diess cautioned, though, that the company could not shield employees from criminal charges.

The amnesty offer is valid through Nov. 30, Mr. Diess wrote, according to excerpts from the letter reviewed by The New York Times. The offer applies only to workers who are covered by collective bargaining agreements; it excludes top management.

While corporate amnesty programs are rare, the approach has been used successfully in Germany at least once before. Siemens, an electronics and engineering company based in Munich, used such an offer in 2008 to encourage employees to provide information during an investigation into bribery of officials abroad. Dozens of employees came forward.

Legal experts said it is unclear how often corporations in the United States offer job amnesty to employees in investigations. That is because, typically, there is little public reporting about the inquiry, the investigations are conducted quietly within the company, and there is often an effort not to alert large numbers of employees to avoid the possible destruction of evidence.

“It is not a common practice,” said Alexandra Wrage, president of Trace International, a company in Annapolis, Md., that provides advice to companies on compliance issues. “It’s a tacit admission, however, that the usual reporting channels have been ineffective.”

By offering job amnesty, Volkswagen might accomplish two things, said Mike Koehler, a law professor at Southern Illinois University who conducted internal investigations for nearly a decade while in private practice: Demonstrate to law-enforcement agencies that it is pursuing all avenues in its internal investigation, and reach out beyond the company’s executive ranks to better understand what happened.

“The amnesty program is not so much designed for the people who are viewed as culpable actors, but rather, for the midlevel people who may have, without even knowing it, some relevant information,” Mr. Koehler said. “That kind of information may be minor in scope, but it’s the cumulative effect — the pieces of minor information put together lead to a more defined picture for the company.”

At Volkswagen, an internal whistle-blower was responsible for uncovering the exaggerated carbon-dioxide and fuel-economy claims, which the company disclosed last week. German news media reports have said that internal investigators looking into the emissions-cheating software, which came to light in September, have been hampered by a reluctance among employees to come forward.

By setting a tight deadline, Volkswagen may be trying to pressure people with knowledge to speak up soon. The internal investigation is being conducted by Jones Day, a law firm.

“Every single day counts,” Mr. Diess wrote. “We are counting on your cooperation and knowledge as our company’s employees to get to the bottom of the diesel and CO2 issue.”

Volkswagen previously had an internal ombudsman’s office that employees could go to with concerns. The company did not have a formal amnesty program until Thursday.

Analysts and people with knowledge of the investigation said it was likely that a substantial number of people were involved in creating and installing the software, and that a larger group may have been aware of it and failed to take action. The software was installed on several generations and types of diesel engines from the 2009-15 model years.

Prosecutors in Braunschweig, a city near Volkswagen’s base in Wolfsburg, have been investigating the case, and have not made any arrests.

Although the company said it could not offer amnesty from criminal prosecution, if employees who come forward later faced criminal charges, “we will draw the attention of the authorities to the willingness to cooperate,” Mr. Diess wrote. “Past experience has shown this speaks in the employee’s favor.”

He also said that Volkswagen reserved the right to transfer employees who come forward to another job, or to give them different responsibilities.

Also on Thursday, Martin Winterkorn, who resigned as chief executive of Volkswagen in September within days of the emissions cheating coming to light, has cut his last formal tie with the carmaker by resigning as chairman of the supervisory board of its Audi division. Julio Schuback, an Audi spokesman, confirmed on Thursday that Mr. Winterkorn resigned on Wednesday. Mr. Schuback said he could not comment on why Mr. Winterkorn remained on the board for more than a month after resigning as chief executive.

Mr. Winterkorn, who stepped down in September, maintained that he had been unaware that software in the diesel vehicles was designed to deceive regulators. The software could recognize when a car was being tested and turn up emissions controls.

At the other times, the cars emitted up to 40 times the amount of nitrogen oxide allowed by United States regulations. The cars had better performance and fuel economy when the emissions controls were turned down.

Under German law, members of a company’s supervisory board can be removed only by shareholders, so it would have been legally cumbersome to force Mr. Winterkorn to leave the Audi board.

Volkswagen owns 99.5 percent of Audi shares, but a small number are still held by outside investors. As a result, Audi must fulfill the legal requirements for companies listed on the stock market. Audi would have had to call a shareholders meeting to remove Mr. Winterkorn.

Volkswagen formed Audi in 1969 by combining two other carmakers, Auto Union and NSU Motorenwerke, which earlier in their histories had been independent.

A version of this article appears in print on , on Page B1 of the New York edition with the headline: Seeking Information, VW Offers Amnesty to Employees . Order Reprints | Today’s Paper | Subscribe